The aim is to determine the structural determinants of polypeptide ligand interaction with nicotinic acetylcholine receptors. The long term goals are to develop the polypeptide neurotoxins as tools for studying receptors and receptor-mediated processes and to develop a picture of the ligand binding surface of the receptor through precise and detailed knowledge of the ligand surface. A major impediment is that the receptors are integral membrane proteins and do not succumb easily to the usual methods of structural analysis. This research approaches the problem from an alternative viewpoint, that of a highly specific tight binding ligand. A major part of this research involves investigations of the contribution of specific parts of the polypeptide toxins to physiologic effect by site directed mutagenesis techniques. Mass spectrometry is used to characterize the mutated products. A second goal is the development of more efficient expression systems for polypeptide neurotoxins so that larger amounts can be more easily produced. Mass spectrometry is used to characterize the mutated products.